1. Field of the Invention
The present invention relates to a secondary battery. More particularly, it relates to a high-voltage secondary battery module having a large capacity with improved unit cell connection.
2. Related Art
Recently, a high-voltage secondary battery using a high energy-density non-aqueous electrolyte is under development. A plurality of high-voltage secondary cells, which will be referred to as unit cells for the sake of convenience hereinafter, are connected in series to thereby form one module to be used for a device that requires high voltage, such as electric vehicle.
Conventionally, each of the unit cells includes an electrode assembly having a positive electrode and a negative electrode with a separator between them; a case having a space for housing the electrode assembly; a cap assembly joined with the case to seal the case; and terminals including a positive terminal and a negative terminal which protrude from the cap assembly to be electrically connected to the positive electrode and the negative electrode of the electrode assembly.
In order to integrate the unit cells into a module, the unit cells are arranged in such a manner that the positive terminal and the negative terminal of each unit cell are alternated with the positive terminal and the negative terminal of neighboring unit cells, and the terminals should be connected to each other by using conductive connectors.
Herein, the conductive connectors are penetrated by the terminals and fixed firmly by nuts so that they do not come out of the terminals. For the firm connection, a screw thread is formed in the external circumference of each terminal.
As described above, the conventional secondary battery module is formed by electrically connecting several to tens of unit cells by using the conductive connectors in the screw engagement method.
In the conventional secondary battery module, only when heat generated in each unit cell is emitted easily, the unit cells can be operated ideally and used smoothly in a device that is operated upon electric power from the battery module, e.g., a hybrid electric vehicle (HEV). Therefore, it can be said that heat emission is the most important factor in the secondary battery module applied to a high-voltage device.
To sum up, if heat is not emitted properly from the unit cells of the secondary battery module, the temperature of the battery module is raised as well as the temperature of each unit cell itself, and this leads to malfunction of the high-voltage device.
Therefore, when the secondary battery module is designed, required is a structure that can increase the heat emitting efficiency in each unit cell. For this, the unit cells need to be arranged with a uniform space between them.
In addition, when the secondary battery module is designed, the cap assembly of each unit cell needs be insulated from the conductive connector in the connection of the unit cells.
If the cap assembly and the conductive connector are not insulated properly, electric short occurs between them, thus degrading the performance of the entire battery module as well as the unit cell of the problem and causing malfunction.
However, the known secondary battery modules fail to maintain a uniform space between the unit cells. Moreover, since the spacing between the unit cells and the insulation between the cap assembly and the conductive conductor are achieved by using different parts individually, the entire structure and assembling process of the secondary battery module is complicated. In particular, since a secondary battery module for driving a motor of a hybrid electric vehicle has dozens of unit cells, when the above problems occur, the damage is even greater.